1. Field of the Invention
The invention involves semiconductor devices and methods for fabricating the same. In particular, the invention involves semiconductor devices having metal oxide semiconductor field effect transistors (MOSFETS) and methods of manufacturing such devices.
2. Description of the Related Art
Increased performance requirements have led to integrated circuits with denser arrays of devices, necessitating for example smaller gate sizes. As gate sizes decrease, forming electrical contacts with gate electrodes becomes an increasingly difficult problem.
In addition, another difficulty in the manufacture of semiconductor devices involves the doping of semiconductor substrate layers with electrically-active materials, in order to form electrically-conductive regions such as source and drain regions in the vicinity of a gate, for example in forming a metal oxide semiconductor field effect transistor (MOSFET). In the creation of such electrically-conductive regions, it is desirable for a shallow, relatively lightly-doped channel or extension region to be closest to the gate. Therefore the doping to create source and drain regions may involve multiple steps: an initial light doping, formation of a mask layer to protect the channels or extensions from further doping, a higher-energy doping to create the main source and drain regions, and finally removal of the mask layer.
From the foregoing, it will be appreciated that it would be desirable to provide simple means for making electrical connections with gate electrodes.
In addition, it will be appreciated that it would be desirable to simplify the procedures for implantation to create source and drain regions.
A semiconductor device includes a T-shaped gate electrode. The T-shaped electrode may have a metal upper layer and a semiconductor lower layer with a diffusion barrier therebetween. The metal upper layer may be used as a gate mask to control implantation of ions in a semiconductor substrate. Gate metal-semiconductor portions may be electrically coupled to both the metal upper portion and the semiconductor lower portion thereby to reduce electrical resistance in the T-shaped electrode. A method of forming source and drain regions in the semiconductor device includes using the T-shaped gate electrode as an implant mask.
According to an aspect of the invention, a semiconductor device has a T-shaped gate electrode with a tungsten top layer.
According to another aspect of the invention, a semiconductor device has a T-shaped gate electrode, the T-shaped gate electrode having a metal upper portion, a semiconductor lower portion, and a gate metal-semiconductor portion electrically coupled both to the upper portion and the lower portion.
According to yet another aspect of the invention, a semiconductor device has a gate electrode which includes a metal portion and a metal-semiconductor portion electrically coupled to the metal portion, the metal of the metal portion being a different metal than the metal of the metal-semiconductor portion.
According to still another aspect of the invention, a semiconductor device has a T-shaped electrode used as an implant mask.
According to a further aspect of the invention, a semiconductor device has a gate electrode which has a metal portion used as an implant mask.
According to a still further aspect of the invention, a method of forming source and drain regions in a semiconductor substrate includes forming deep implant regions using a perpendicular implant, and forming extensions or channels using one or more tilted implants.
According to another aspect of the invention, a method of forming source and drain regions in a semiconductor substrate includes using a gate electrode as an implant mask during the formation of deep implant regions.
According to yet another aspect of the invention, a method for fabricating a semiconductor device includes the steps of forming a T-shaped gate electrode over a semiconductor substrate, the gate electrode having a metal upper portion which overhangs a conductive lower portion; and selectively implanting an exposed surface of the substrate, using the metal upper portion as an implant mask.
According to still another aspect of the invention, a semiconductor device includes a T-shaped gate electrode having a lower conductive portion and an upper conductive portion with overhangs that overhang the lower portion, the upper portion including tungsten.
According to a further aspect of the invention, a semiconductor device includes a gate electrode having a lower semiconductor portion, an upper metal portion, a diffusion barrier between the lower portion and the upper portion, and a metal-semiconductor portion electrically coupled to the lower portion and the upper portion.
According to a still further aspect of the invention, a method of fabricating a semiconductor device includes the steps of forming a gate electrode over a semiconductor substrate, the gate electrode having a metal upper portion and a semiconductor lower portion; and forming a metal-semiconductor portion on the gate electrode which is electrically coupled to the lower portion and the upper portion.
To the accomplishment of the foregoing and related ends, the invention comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.